[1.0.X] Fixed #9626 -- Fixed a deletion race in the locmem cache.

Backport of r9998 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@10001 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/core/cache/backends/locmem.py

@@ -96,8 +96,11 @@ class CacheClass(BaseCache):
 
         self._lock.writer_enters()
         try:
-            del self._cache[key]
-            del self._expire_info[key]
+            try:
+                del self._cache[key]
+                del self._expire_info[key]
+            except KeyError:
+                pass
             return False
         finally:
             self._lock.writer_leaves()